Process of manufacturing light-polarizing material



XR zasaeas BUMV PROCESS OF MANUFACTURING LIGHT- POLARIZING MATERIAL Edwin H. Land, Cambridge, Mass, assignor to Polaroid Corporation, Dover, Del., a corporation of Delaware No Drawing. Application December 22, 1941,

'7 Claims.

This invention relates to a new and improved process for the manufacture of light-polarizing materials.

An object of the invention is to provide a process of the character described wherein orientable light-polarizing crystals, for example asymmetric crystals of herapathite or other lightpolarizing material, are introduced into a thermoplastic, transparent, suspending medium which is subjected while plastic to a force which orients in substantial parallelism the crystals suspended therein.

A further object of the invention is to provide such a process in which the suspending medium is set or hardened while the polarizing crystals therein are oriented to substantial parallelism so as to produce a light-polarizing body.

A still further object of the invention is to provide a process of the character described wherein a substantially uniform,thin layer of a suspension of the character described is subjected to mechanical force to orient the suspended crystals.

Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, as exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

In my issued Patent No. 1,951,664, granted March 20, 1934, for colloidal suspensions and the process of making same, I disclose a process for the manufacture of colloidal herapathite. The product of that process is described as a jellylike suspension of minute, needle-shaped or fibershaped colloidal crystals in methyl alcohol.

Such a suspension may be employed in the process of the present invention. Where it is employed, it is preferably dried out to some extent and then mixed into a mass of a heated, thermoplastic, transparent, suspending medium such for example as Canada balsam.

'I'ne colloidal polarizing crystals are preferably thoroughly dispersed throughout the suspending medium, as by mixing therein vigorously, and any methyl alcohol or other liquid which may have been introduced into the mixture with the polarizing crystals is then evaporated so that what remains is a suspension of minute, needle-shaped, polarizing crystals in a transparent, thermoplastic, suspending medium.

Orientation of the crystals within the medium may be effected by subjecting the suspension to a force to which the crystals are responsive. For

Serial No. 424,085

example, the suspension while in viscous plastic form may be subjected to stretch preferably after first having been shaped to a substantially uniform, relatively thin layer. Or the suspension may be subjected to a smearing action or a rolling action or some other mechanical force tending to orient the polarizing crystals therein with their needle axes in substantial parallelism.

While the crystals are in parallel orientation within the suspension, it is preferably hardened as by cooling so as to hold the crystals permanently in oriented relation.

It should be understood that the crystals may be oriented in the suspending medium substantially at the time they are introduced therein and before the medium is permitted to cool, or, if desired, the crystals may be introduced into the suspending medium and the mass then permitted to cool, and thereafter orientation of the crystals within the medium may be effected by heating the suspension to a point at which the medium becomes plastic, and then subjecting it to a force to align the crystals therein.

It should be understood, furthermore, that where the crystals are of such a nature as to be responsive to an impressed electric or magnetic field, for example where crystals of herapathite are employed, orientation may be effected in this manner.

While Canada balsam has been described as the suspending medium, it is to be understood that other materials may be used. It is necessary only that the suspending medium be lighttransmitting and plastic at temperatures below those at which the suspended light-polarizing crystals are destroyed or lose their polarizing properties. For example, certain of the vinyl compounds and more specifically plasticized polymerized vinylacetate may be employed to advantage as the suspending medium even with light-polarizing crystals which decompose at temperatures of about 200 degrees C.

So also, while herapathite has been described as the material of which the suspended lightpolarizing crystals is formed, it is to be understood that other materials may be employed. For example, inorganic polarizing crystals such as purpureocobaltcliloridesulphateperiodide may be used. 1 F 4 Furthermore, while the suspended crystals have been described as needle-shaped or threadlike in form, it is to be understood that such a form or habit is desirable primarily only where the suspension is to be subjected to a mechanical force to orient the suspended crystals. Where tie-Elihu N Since certain changes in carrying out-the above process and certain modifications thereof may be made without departing fromits, scope, it is intended that all matter contained inthe above description shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein.

described, and all statements of. the scope of the invention which, as a matter of language, might be said'to fall therebetween.

What is claimed is:

1. The process of making a light-polarizing body which comprises heating a plastic material having light-transmitting properties and containing orientable light polarizing crystals, applying to a thin layer thereof, while it is heated, a force to which said crystals are responsive for such duration as to align said crystals in parallelism, and permitting said plastic material to cool, thereby holding said crystals in permanent parallel alignment. I

2. The process of making a light-polarizing body which comprises heating; a plastic 'material having lighttransmitting properties and containing orientable lights-polarizing crystals, applying to a thinlayer thereof, while it'is heated, a uniform mechanical forcefor such duration as to align said crystalsin parallelism, andpermitting said plastic material to cool, thereby holding said, crystals in permanent parallel alignment.v a

3. The; process of, making a light-polarizing body which comprises heating, a transparent, suspending, medium containingorientable lightpolarizing crystals until said. medium, becomes body which comprises heating a light-transmitting, thermoplastic material to a temperature at which it is in a plastic state, incorporating therein a multipliicty of orientable, light-polarizing crystals, forming a substantially uniform, thin layer of said medium and thesuspended crystals, orienting said crystals within said suspending medium, and cooling said medium to set said oriented crystals in permanent alignment.

6. 'The process of making a light-polarizing body which comprises heating a material having light-transmitting properties and containing orientable light-polarizing molecules until saidmaterial is in a plastic state, applying a uniform mechanical force to a thin layerofisaid material while it is in a plastic state and in such direction and to such an extent as to. align 'said' molecules in parallelism, and subsequently'cooling' said thin layer of plastic material to. set said molecules in permanent alignment.

'7. The processv of making. a light-polarizing body which'comprises heating, a material'having light-transmitting properties and, containing orientable lightepolarizing crystals until said material is in a, plastic state, applyin'gla'; uniform mechanical forceto athin layer ofsaid material while it is ina plastic state. and'in, suclidirection and to such an extent as to align said crystals in parallelism, and subsequently. cooling said thin layer of plastic material toset} said crystals in permanent alignment. 

